In a typical cellular radio system, wireless terminals (also known as mobile stations and/or user equipments (UEs)) communicate via a radio access network (RAN) to one or more core networks. The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” (UMTS) or “eNodeB” (LTE). A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units (UE) within range of the base stations.
In some versions of the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a controller node (such as a radio network controller (RNC) or a base station controller (BSC)) which supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). UTRAN is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. The 3GPP has developed specifications for the Evolved Packet System (EPS). The Evolved Packet System comprises an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as Long Term Evolution (LTE) access technology and Evolved Packet Core (EPC). Long Term Evolution (LTE) is a variant of a 3GPP radio access technology wherein the radio base station nodes are connected to a core network rather than to radio network controller (RNC) nodes.
A main component of the EPS is the Evolved Packet Core (EPC), also known as SAE Core. The EPC serves as equivalent of GPRS networks via the Mobility Management Entity (MME), Serving Gateway (SGW) and Packet Data Network (PDN) Gateway subcomponents, each discussed briefly below.
FIG. 1 shows an example implementation of the aforementioned Evolved Packet System as comprising for example the E-UTRAN and the Mobility Management Entity (MME) in the EPC. The mobility management entity (MME) handles various control functions. The nodes and LTE/SAE or Evolved Packet System (EPS) architecture of FIG. 1 and other architecture scenarios are understood with reference to 3GPP TS 23.401, which provides, e.g., a system architecture description.
In some of its implementations, the E-UTRAN may comprise a number of different base stations, e.g., eNodeBs (eNBs). A S1-MME interface/reference point is used for control signaling between the eNBs and the mobility management entity (MME). An eNB may have 51 links to multiple MMEs in case the MME pool concept is used. The user plane data goes via the Serving GateWay (SGW) on a S1-U interface/reference point. Between eNBs a X2 interface/reference point is used.
The MME (Mobility Management Entity) is responsible for idle mode UE (User Equipment) tracking and paging procedure including retransmissions; is involved in the bearer activation/deactivation process; and, is also responsible for choosing the SGW for a UE at the initial attach and at time of intra-LTE handover involving Core Network (CN) node relocation. The MME is also responsible for authenticating the user (by interacting with the HSS). The Non Access Stratum (NAS) signaling terminates at the MME and it is also responsible for generation and allocation of temporary identities to UEs. Among its other functions, the MME is the termination point in the network for ciphering/integrity protection for NAS signaling and handles the security key management.
The SGW (Serving Gateway) routes and forwards user data packets, while also acting as the mobility anchor for the user plane during inter-eNodeB handovers and as the anchor for mobility between LTE and other 3GPP technologies. For idle state UEs, the SGW terminates the downlink data path and triggers paging when downlink data arrives for the UE. The SGW manages and stores UE contexts, e.g. parameters of the IP bearer service and network internal routing information. The SGW also performs replication of the user traffic in case of lawful interception.
The PGW (PDN Gateway) provides connectivity from the UE to external packet data networks by being the point of exit and entry of traffic for the UE. The PGW performs policy enforcement, packet filtering for each user, charging support, lawful interception and packet screening.
An ePDG (Evolved Packet Data Gateway) essentially secures data transmission with a UE connected to the EPC over an untrusted non-3GPP access.
In general, in LTE the functions of a radio network controller (RNC) node are distributed between the radio base stations nodes (eNodeBs in LTE) and access gateways (AGWs), such as the SGW. As such, the radio access network (RAN) of an LTE system has an essentially “flat” architecture comprising radio base station nodes without reporting to radio network controller (RNC) nodes.
An issue with current use of LTE networks is that the traffic model has changed and now includes a significantly higher frequency of Service Request executions. Use of smart phones is a large contributor to this change.
A high frequency in Service Request executions cause a high load primarily to the SGW, but also to the MME as it is required to verify and provide bearer contexts to the eNodeB. The high signaling load at the SGW and possibly at the MME can lead to capacity bottlenecks, and reduce the operator's overall network performance. In extreme cases, this can also lead to network outages. This problem has caused network capacity limitations and operators are concerned.
The Radio Resource Control (RRC) sub-layer in 3GPP LTE performs control-plane functions such as broadcast of system information related to access stratum and non-access stratum, paging, establishment, maintenance and release of an RRC connection between the User Equipment (UE) and E-UTRAN, signaling radio bearer management, security handling, mobility management including UE measurement reporting and configuration, active mode handover, idle mode mobility control, Multimedia Broadcast Multicast Service (MBMS) notification services and radio bearer management for MBMS, Quality of Service (QoS) management and NAS direct message transfer between NAS and UE. A 3GPP LTE compliant UE has two steady-state operational states: RRC_CONNECTED and RRC_IDLE. A UE is in RRC_CONNECTED when an RRC connection or control-plane has been established. If this is not the case, i.e. no RRC connection is in place, the UE is in RRC_IDLE state.
In current procedures, a device is moved from connected state to idle state after a timeout of inactivity. Being in the idle state helps to reduce terminal battery consumption, as the terminals consume significantly less power in idle mode when their radio bearers have been released. It also helps reducing the load on the radio access network. However, moving a terminal from connected to idle mode, and then back from idle to connected, causes a lot of signaling, since the S1 release, service request and paging procedures in LTE incur a significant signaling overhead.
Since operators minimizing the time radio resources are used, and since the connected mode discontinuous reception (DRX) technology is not yet available, operators tend to configure a short inactivity time to quickly move terminals back to idle mode again. Even with connected mode DRX technology available, some operators may prefer to minimize the number of simultaneously RRC-connected mode terminals in an eNB, and therefore force a quick transition back to idle mode for terminals. However, depending on traffic pattern, a quick transition back to idle mode creates a problem with frequent connected-idle signaling resulting in a high signaling load.